1. Field of the Invention
The present invention relates to a vehicle control system for performing a steerage control based on an azimuth change quantity of a road calculated from map information and a position of a subject vehicle.
2. Description of the Related Art
There is a technique conventionally known from Japanese Patent Application Laid-open No.89298/85, which determines whether the subject vehicle can pass through a curve existing ahead of the subject vehicle in a traveling direction at a current vehicle speed, by estimating a radius of curvature of the curve based on map data obtained by a navigation system, and gives a warning to a driver, when it is determined that the subject vehicle cannot pass through the curve.
In the above known technique, however, it is only determined whether the vehicle can pass through the curve at the current vehicle speed, and a misalignment of the vehicle from the curvature of the road is not detected, resulting in a problem that a proper warning is difficult. Moreover, even if a warning is given when the driver has a lowered driving capability due to a fatigue or when the driver is inattentively driving the vehicle, a driver's quick steering or braking operation is required to avoid the departing of the vehicle from the road, and an unskilled driver cannot cope with such operation, resulting in a possibility that the vehicle will depart from the road.
There are conventionally proposed various follow-up travel control systems which are designed to detect a vehicle traveling ahead of a subject vehicle (which will be referred to as an ahead-traveling vehicle hereinafter) by radar or the like and perform a vehicle-vehicle distance control so that a distance between the subject vehicle from the ahead-traveling vehicle is maintained constant. However, if a control for preventing the departing of the vehicle from the road and a follow-up travel control for permitting the vehicle to travel while following the ahead-traveling vehicle are conducted simultaneously, for example, if a steerage control started when the driver is conducting the steerage to cause the subject vehicle to trace a travel locus of the ahead-traveling vehicle during the follow-up travel control, it is considered that the driver feels a sense of incompatibility. If the arrangement is such that both of the controls are switched from one to another at each time by a manual operation, for example, when the driver has lost sight of the ahead-traveling vehicle during the follow-up travel control, the following problems are encountered: the driver may forget the switching-over to the control for preventing the departing of the subject vehicle from the road, and such switching-over is troublesome for the driver.
There is also a technique known from Japanese Patent Application Laid-open No.5-113822, which detects an obstacle existing ahead of the subject vehicle on a travel road by a video camera or radar, and conducts a vehicle speed control or a steerage control to avoid the collision of the subject vehicle against the obstacle, when it is determined that there is a possibility of the collision of the vehicle against the obstacle.
If the obstacle-avoiding control system is combined with the steerage control system designed to determine whether there is a possibility of the departing of the vehicle from the road, based on the traveling state of the vehicle and the shape of a road district existing ahead of a subject-vehicle position on a travel road, and to apply a steering torque to a steering means, when it is determined that there is the possibility of the departing of the vehicle from the road, thereby preventing the departing of the vehicle from the road, the following problem is encountered: both of the controls interfere with each other to make it difficult to perform a smooth avoidance of the obstacle.
Specifically, when the driver conducts the steerage to avoid the obstacle, the vehicle departs from an intrinsic course and hence, the steerage control system applies a steering torque to the steering means to return the vehicle to the original course. However, this steering torque is in a direction opposite from a direction of a steering torque applied by the driver to avoid the obstacle, and hence, there is a possibility that the burden of the driver's obstacle-avoiding operation is increased and that a sense of incompatibility is imparted.